U.S. patent application number 15/228124 was filed with the patent office on 2018-02-08 for textured fuel cell components for improved water management.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Kerrie K. GATH, Mark Stephen RICKETTS, Daniel E. WILKOSZ.
Application Number | 20180040905 15/228124 |
Document ID | / |
Family ID | 61069892 |
Filed Date | 2018-02-08 |
United States Patent
Application |
20180040905 |
Kind Code |
A1 |
WILKOSZ; Daniel E. ; et
al. |
February 8, 2018 |
TEXTURED FUEL CELL COMPONENTS FOR IMPROVED WATER MANAGEMENT
Abstract
A fuel-cell stack including treated bipolar plates is disclosed,
as well as methods of treatment. The bipolar plates may include an
active region wherein a fuel-cell reaction is configured to occur
and an inactive region configured to supply, collect, and remove
fluids from the active region. The inactive region may include one
or more exit vias defined by the bipolar plate and having an inner
surface configured to contact fluids received from the active
region. At least a portion of the inner surface may have a
hydrophobic textured surface. The methods may include treating a
metal inner surface of an exit via defined in an inactive region of
a fuel-cell bipolar plate that is configured to contact fluids
received from an active region of the fuel-cell bipolar plate. The
treatment may include removing material to form a hydrophobic
textured surface on at least a portion of the inner surface.
Inventors: |
WILKOSZ; Daniel E.; (Saline,
MI) ; GATH; Kerrie K.; (Pittsfield, MI) ;
RICKETTS; Mark Stephen; (Windsor, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
61069892 |
Appl. No.: |
15/228124 |
Filed: |
August 4, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/04253 20130101;
H01M 8/0258 20130101; Y02E 60/50 20130101; H01M 8/04156 20130101;
B23K 26/355 20180801; H01M 2008/1095 20130101; H01M 8/0206
20130101; B23K 26/352 20151001 |
International
Class: |
H01M 8/0256 20060101
H01M008/0256; B23K 26/352 20060101 B23K026/352; C23F 1/14 20060101
C23F001/14; B23K 26/00 20060101 B23K026/00; H01M 8/04291 20060101
H01M008/04291; H01M 8/04223 20060101 H01M008/04223 |
Claims
1. A fuel-cell bipolar plate, comprising: an active region wherein
a fuel-cell reaction is configured to occur; and an inactive region
configured to supply, collect, and remove fluids from the active
region; the inactive region including one or more exit vias defined
by the bipolar plate and having an inner surface configured to
contact fluids received from the active region, at least a portion
of the inner surface having a hydrophobic textured surface.
2. The bipolar plate of claim 1, wherein substantially the entire
inner surface has the hydrophobic textured surface.
3. The bipolar plate of claim 1, wherein the hydrophobic textured
surface includes a plurality of cone-shaped surface features.
4. The bipolar plate of claim 3, wherein the surface features have
a maximum width of less than 250 .mu.m.
5. The bipolar plate of claim 3, wherein the surface features have
a maximum width of 50 nm to 50 .mu.m.
6. The bipolar plate of claim 1, wherein the hydrophobic textured
surface has a contact angle with water of at least 100 degrees.
7. The bipolar plate of claim 1, wherein the inactive region
further includes a transition region defined by the bipolar plate
and disposed between the active region and the one or more exit
vias, the transition region including one or more channels or
features configured to transport and guide fluids from the active
region to the exit vias.
8. The bipolar plate of claim 7, wherein at least a portion of the
one or more channels or features in the transition region has a
hydrophobic textured surface.
9. The bipolar plate of claim 8, wherein the hydrophobic textured
surface includes a plurality of cone-shaped surface features having
a maximum width of less than 250 .mu.m.
10. The bipolar plate of claim 1, wherein a smallest dimension of
the one or more exit vias is at most 0.50 mm.
11. A method, comprising: treating a metal inner surface of an exit
via defined in an inactive region of a fuel-cell bipolar plate that
is configured to contact fluids received from an active region of
the fuel-cell bipolar plate; and the treatment including removing
material to form a hydrophobic textured surface on at least a
portion of the inner surface.
12. The method of claim 11, wherein the treatment forms a plurality
of cone-shaped surface features.
13. The method of claim 11, wherein the treatment forms surface
features having a maximum width of less than 250 .mu.m.
14. The method of claim 13, wherein the surface features have a
maximum width of 50 nm to 50 .mu.m.
15. The method of claim 11, wherein the treating step includes
removing material from the metal inner surface using a laser
treatment.
16. The method of claim 11, wherein the treating step includes
removing material from the metal inner surface using a chemical
treatment.
17. The method of claim 11, wherein the treatment is applied to the
entire inner surface of the exit via.
18. The method of claim 11, further comprising treating at least
one metal channel surface of a transition region of the inactive
region of the fuel-cell bipolar plate that is disposed between the
exit via and the active region, the treatment forming a hydrophobic
textured surface on at least a portion of the channel surface.
19. The method of claim 11, wherein the bipolar plate includes a
plurality of air exit vias defined therein and the treating step
includes treating a metal inner surface of each air exit via to
form a hydrophobic textured surface on at least a portion of the
inner surface.
20. A fuel-cell bipolar plate, comprising: an active region; an
inactive region configured to supply, collect, and remove fluids
from the active region, the inactive region including an exit via
defined by the bipolar plate and having a width of at most 3.0 mm,
an inner surface of the exit via configured to contact fluids
received from the active region; and at least a portion of the
inner surface having a hydrophobic textured surface.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to textured fuel cell
components for improved water management, for example, water
removal and ice prevention.
BACKGROUND
[0002] Fuel cells, for example, hydrogen fuel cells, are one
possible alternative energy source for powering vehicles. In
general, fuel cells include a negative electrode (anode), an
electrolyte, and a positive electrode (cathode). In a proton
exchange membrane fuel cell (PEMFC), the electrolyte is a solid,
proton-conducting membrane that is electrically insulating while
allowing for protons to pass through. Typically, the fuel source,
such as hydrogen, is introduced at the anode using flow field
passages of the anode side of a bipolar platewhere it reacts with a
catalyst and splits into electrons and protons. The protons travel
through the electrolyte to the cathode side of the membrane and the
electrons pass through the bipolar plate or through an external
circuit to the cathode. At the cathode, oxygen in air introduced
from the cathode side of a bipolar plate reacts with the electrons
and the protons at another catalyst to form water. One or both of
the catalysts are generally formed of a noble metal or a noble
metal alloy, typically platinum or a platinum alloy. During
operation of a fuel cell, various levels of water may be generated
on and along the fuel cell stack components, such as along or
within plate flow field channels or other plate features and fuel
cell plate interfacing surfaces. Some fuel cell systems may include
gas/air flow pressure drops or other system operation control
practices in an attempt to manage/remove generated water from the
fuel cell plates. However, residual moisture may condense from cell
surfaces and/or collect, producing water deposits along fuel cell
surfaces that can remain after stack shut down. If exposed to
subzero degree Celsius ambient conditions, this residual
moisture/water can form ice blockages to gas flow paths. Ice
formation can be detrimental to stack component durability and
operation efficiency, especially at start up.
SUMMARY
[0003] In at least one embodiment, a fuel-cell bipolar plate is
provided. The bipolar plate may include an active region wherein a
fuel-cell reaction is configured to occur and an inactive region
configured to supply, collect, and remove fluids from the active
region. The inactive region may include one or more exit vias
defined by the bipolar plate and having an inner surface configured
to contact fluids received from the active region. At least a
portion of the inner surface may have a hydrophobic textured
surface.
[0004] In one embodiment, substantially the entire inner surface
has the hydrophobic textured surface. The hydrophobic textured
surface may include a plurality of cone-shaped surface features. In
one embodiment, the surface features have a maximum width of less
than 250 .mu.m. In another embodiment, the surface features have a
maximum width of 50 nm to 50 .mu.m. The hydrophobic textured
surface may have a contact angle with water of at least 100
degrees. The inactive region may further include a transition
region defined by the bipolar plate and disposed between the active
region and the one or more exit vias, the transition region
including one or more channels or features configured to transport
and guide fluids from the active region to the exit vias. At least
a portion of the one or more channels or features in the transition
region may include a hydrophobic textured surface. The hydrophobic
textured surface may include a plurality of cone-shaped surface
features having a maximum width of less than 250 .mu.m. In one
embodiment, a smallest dimension of the one or more exit vias is at
most 0.50 mm.
[0005] In at least one embodiment, a method is provided. The method
may include treating a metal inner surface of an exit via defined
in an inactive region of a fuel-cell bipolar plate that is
configured to contact fluids received from an active region of the
fuel-cell bipolar plate. The treatment may include removing
material to form a hydrophobic textured surface on at least a
portion of the inner surface.
[0006] The treatment may form a plurality of cone-shaped surface
features. In one embodiment, the treatment forms surface features
having a maximum width of less than 250 .mu.m. The surface features
may have a maximum width of 50 nm to 50 .mu.m. The treating step
may include removing material from the metal inner surface using a
laser treatment or using a chemical treatment. In one embodiment,
the treatment is applied to the entire inner surface of the exit
via. The method may include treating at least one metal channel
surface of a transition region of the inactive region of the
fuel-cell bipolar plate that is disposed between the exit via and
the active region, the treatment forming a hydrophobic textured
surface on at least a portion of the channel surface. The bipolar
plate may include a plurality of air exit vias defined therein and
the treating step may include treating a metal inner surface of
each air exit via to form a hydrophobic textured surface on at
least a portion of the inner surface.
[0007] In at least one embodiment, a fuel-cell bipolar plate is
provided. The bipolar plate may include an active region and an
inactive region configured to supply, collect, and remove fluids
from the active region. The inactive region may include an exit via
defined by the bipolar plate and having a width of at most 3.0 mm,
and an inner surface of the exit via may be configured to contact
fluids received from the active region. At least a portion of the
inner surface may have a hydrophobic textured surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is an exploded view of a proton exchange membrane
fuel cell (PEMFC) unit cell, according to an embodiment;
[0009] FIG. 2 is a cross-section of a PEMFC showing the components
of the anode, cathode, and proton exchange membrane, according to
an embodiment;
[0010] FIG. 3 is a perspective view of a PEMFC bipolar plate,
according to an embodiment;
[0011] FIG. 4 is a perspective view of another embodiment of a
PEMFC bipolar plate; and
[0012] FIGS. 5A and 5B are schematic cross-section examples of
hydrophobic textured surface patterns.
DETAILED DESCRIPTION
[0013] As required, detailed embodiments of the present invention
are disclosed herein; however, it is to be understood that the
disclosed embodiments are merely exemplary of the invention that
may be embodied in various and alternative forms. The figures are
not necessarily to scale; some features may be exaggerated or
minimized to show details of particular components. Therefore,
specific structural and functional details disclosed herein are not
to be interpreted as limiting, but merely as a representative basis
for teaching one skilled in the art to variously employ the present
invention.
[0014] With reference to FIGS. 1 and 2, an example of a proton
exchange membrane fuel cell (PEMFC) 10 unit cell is illustrated.
The PEMFC 10 unit cell generally includes a negative electrode
(anode plate) 22' and a positive electrode (cathode plate) 22'',
separated by a membrane electrode assembly (MEA) 11. As depicted in
FIGS. 1 and 2, the MEA 11 can be made up of anode side 12 and
cathode side 14 components, such as gas diffusion layers (GDL) 18'
and 18'' and catalyst layers 20' and 20'' separated by a proton
exchange membrane (PEM) 16 (also called a polymer electrolyte
membrane). Anode 22' and cathode 22'' plates generally possess
channel geometries 24 used to distribute gases during operation.
Catalyst layers 20' and 20'' may be the same for both the anode
side 12 and cathode side 14 of the MEA 11. Catalyst layers may also
be different between the anode side 12 and cathode side 14 of the
MEA 11. The catalyst layer 20' may facilitate the splitting of
hydrogen atoms into hydrogen ions and electrons while the catalyst
layer 20'' facilitates the reaction of oxygen gas, hydrogen ions,
and electrons to form water. In addition, the MEA 11 may include an
anode side 26' and cathode side 26'' microporous layer (MPL)
disposed between respective GDL layers 18 and catalyst layers
20.
[0015] The PEM 16 may be any suitable PEM known in the art, such as
a fluoropolymer, for example, Nafion (a sulfonated
tetrafluoroethylene based fluoropolymer-copolymer). The GDL 18 may
be formed of materials and by methods known in the art. For
example, the GDL 18 may be formed from carbon fiber based paper
and/or cloth. GDL materials are generally highly porous (having
porosities of about 80%) to allow reactant gas transport to the
catalyst layer (which generally has a thickness of about 8-15
.mu.m), as well as liquid water transport from the catalyst layer.
GDLs may be treated to be hydrophobic with a non-wetting polymer
such as polytetrafluoroethylene (PTFE, commonly known by the trade
name Teflon). A microporous layer (MPL) may be coated to the GDL
side facing the catalyst layer to assist in water management during
operation. The MPL may be formed of materials and by methods known
in the art, for example, carbon powder and a binder (e.g., PTFE
particles). The catalyst layer 20 may include a noble metal or a
noble metal alloy, such as platinum or a platinum alloy. The
catalyst layer may include a catalyst support, which may support or
have deposited thereon a catalyst material.
[0016] The bipolar plates 22 may have channels 24 defined therein
for carrying gases. The channels 24 may carry air or fuel (e.g.,
hydrogen). As shown in FIG. 1, the plates 22 and channels 24 may be
rotated 90 degrees relative to each other. Alternatively, the
plates 22 and channels may be oriented in the same direction or any
combination thereof. The channels 24 need not be continuous or
follow straight flow paths. Bipolar plate materials need to be
electrically conductive and corrosion resistant under proton
exchange membrane fuel cell (PEMFC) operating conditions to ensure
that the bipolar plate performs its functions--feeding reactant
gases to the membrane electrode assembly (MEA) and collecting
current from the MEA.
[0017] As described in the Background, residual water may be
present in conventional fuel cells despite system-level controls
that attempt to remove or reduce it. Residual water can collect or
puddle in or along various areas of a fuel cell plate, such as in
channels, transition zones or manifold port openings and passages
known as exit and inlet vias that can lead to and from port
openings. Water collection in the vias may be exacerbated due to
their small size or interaction with possible via geometry features
which may result in water being drawn into the vias due to
capillary action. Residual water present in a fuel cell is prone to
freeze at ambient temperatures of 32.degree. F. or below (depending
on ambient pressure). Freezing of water within a fuel cell can
cause component damage and may also act as a blockage to fuel and
air at start-up. If ice blockages exist, they need to be removed or
melted in order for a fuel cell to operate properly. Freeze
start-up procedures may require the use of available fuel or stored
energy and can introduce delay in being able to operate a fuel cell
vehicle. Extended start-up times are also not generally desirable
for customer usage. Freezing of the manifold vias (inlets and
outlets) may be particularly problematic, since ice formation in
the vias may cause a total blockage and prevent any gases upstream
from flowing. Since vias can be the narrowest and/or shallowest
portion of the gas flow path, a relatively small amount of residual
water may result in restricted gas flow and or a large or complete
blockage of gas flow.
[0018] With reference to FIGS. 3-4, examples of a fuel cell bipolar
plate 50 are shown. In general, the bipolar plate 50 may include an
active area 52 and a non-active area 54. The active area 52 may be
defined as the area of the bipolar plate where the reaction occurs
between the hydrogen gas (or other fuel) and oxygen (e.g., air).
The active area 52 may include one or more channels 56 that guide
the fuel or the oxygen, depending on the side of the bipolar plate
50. The non-active area 54 may include the area of the bipolar
plate where gas flow occurs but there are no reactions taking
place. The non-active area may include channels, passages, or other
geometry features such as pillars for management of gases (fuel
and/or oxygen), coolants, or other substances. Water that is
generated in the active area 52 may need to be removed through the
channels or other features in the non-active area 54. In one
embodiment, the non-active area 54 may include a transition area or
zone 58 and an exit area or zone 60. The transition zone 58 may be
disposed between the active area 52 and the exit zone 60.
[0019] The transition zone 58 may include one or more channels,
passages 62, or other features, such as a reservoir, that receive a
fluid from the active area 52. The fluid may be unreacted fuel or
oxygen/air and may also include any water (or other liquids) formed
during the fuel cell reaction. The transition zone 58 may collect
the gases and any liquid from the active zone and guide or funnel
it to the exit zone 60. While a bipolar plate 50 is shown and
described having a transition zone 58, a transition zone 58 is not
required and may not be present in other embodiments. The exit zone
60 may include one or more channels or passages 64 that receive a
fluid from the active area 52 (optionally via a transition zone)
and allow it to be removed from a stack of a plurality of bipolar
plates 50. What happens to the fluid after it leaves the exit zone
60 may depend on the type of fluid (e.g., fuel or oxygen/air) and
the design of the specific fuel cell. For example, if the fluid is
unreacted fuel, it may be collected and recirculated. If the fluid
is air/oxygen, it may be removed from the fuel cell stack and
exhausted (e.g., to the environment). Water or other fluids may be
collected and removed from the system (e.g., exhausted to the
environment).
[0020] The channel passages 64 in the exit zone 60 may also be
referred to as vias 64. Depending on operating conditions and plate
flow field and transition zone design, vias 64 can be narrower or
smaller in size than channels 56 in the active zone or channels 62
in the transition zone 58 (if present). Transition zones may also
be void of channel features and use a type of pillar configuration
instead. Via dimensions can also be larger than neighboring active
zone or transition zone design cross sections. Vias are configured
to help deliver desired gas flow pressures in conjunction with
other plate features during operation of a fuel cell. In addition,
vias are configured to help manage water removal from unit cells of
a stack during operation and shut down. Regardless of dimension,
vias need to address these two plate attributes during fuel cell
operation. Making via surfaces hydrophobic can enhance stack
operating pressure control and water management of fuel cell unit
cells when using any size via. For comparison, an example PEM fuel
cell can have a via width of 1.4 mm to 2.5 mm in compliance with an
active flow field area channel width of 1.0 mm 0.40 mm. Via width
is only one variable of comparison. Flow field channel, transition
zone features and via geometries can also all have different
depths.
[0021] The via depths may be the same depth or smaller than those
of same plate flow field channel depths. For example, the via depth
may be at least 10% less than the flow field channel depths, such
as at least 25% or at least 50% less. In another embodiment, the
via depth may be 10-50% less than the flow field channel depths.
Therefore, as described above, smaller width or shallower depth
vias may be more susceptible to the formation of ice blockages in
cold weather. Accordingly, in at least one embodiment, steps may be
taken to make the via 64 surfaces hydrophobic or super hydrophobic.
A treatment may be performed on the vias 64 to make the surfaces
thereof more hydrophobic. The treatment may be performed on the
vias 64 alone, or the vias 64 and other portions of the bipolar
plate 50. For example, the transition zone 58 may be treated,
including the channels 62. The active area 52 may also be treated,
including the channels 56. Hydrophobic treatment of these
additional areas may further facilitate water removal and may
assist in preventing freezing of the vias 64 and potential
transition zone exit areas leading to the vias. However, in one
embodiment, only the vias 64 may be treated, since they are
generally the shallowest, narrowest, and/or highest risk area for
freezing. In another embodiment, the channels 62 in the transition
zone 58 and the vias 64 may be treated.
[0022] Any suitable treatment may be used to make the walls of the
vias 64 hydrophobic (or increase their hydrophobicity). In at least
one embodiment, the treatment may include altering the surface of
the vias 64 directly (e.g., metal surface). This may mean that the
hydrophobicity is not due to a coating being applied. In at least
one embodiment, no coating is applied to the vias 64. However, in
other embodiments, a hydrophobic coating may be applied to the vias
64. Coatings may wear off over time, while changing the structure
of the via surface may be substantially permanent (at least over
the lifetime of the fuel cell). Therefore, a treatment that alters
the surface structure of the via walls may be more durable and
longer-lasting. In one embodiment, the treated vias 64 may have a
width of up to 3.0 mm, for example, no more than 2.5, 2.0, 1.5 or
1.0 mm. For example, the vias 64 may have a width of 0.5 to 3.0 mm,
or any sub-range therein, such as 0.5 to 2.0 mm, 0.7 to 2.0 mm, 0.7
to 1.5 mm, or 0.8 to 1.2 mm. In another embodiment a smallest
dimension (e.g., width or depth) of the treated vias 64 may be up
to 1.0 mm, for example, no more than 0.75, 0.5, or 0.3 mm. For
example, a smallest dimension (e.g., width or depth) of the treated
vias 64 may be 0.1 to 0.7 mm, or any sub-range therein, such as 0.2
to 0.6 mm or 0.3 to 0.5 mm. However, these dimensions are not
intended to be limiting, and the disclosed treatment may be applied
to vias having larger or smaller dimensions.
[0023] In at least one embodiment, the treatment may be a laser
treatment. It has been found that a laser treatment may be used to
render a metal (e.g., steel, Al, or Cu) surface hydrophobic. The
laser treatment may be a femtosecond pulse laser treatment in which
very short bursts of laser energy are used to alter the surface
structure of a substrate. It is believed that the laser energy
alters or changes the surface of the substrate through a
combination of ablation and reformation. In one embodiment, the
laser treatment may result in a plurality of surface features 70,
which may be arranged in an array. As shown in cross-section in
FIGS. 5A and 5B, example surface features 70 may be cone-shaped
structures. The surface features 70 may have a rounded tip (e.g.,
FIG. 5B), or may be cylindrical structures having a tapered and
possibly rounded tip. In another embodiment, the surface features
70 may be a tapered stepped structure, similar to a block pyramid,
or other hydrophobic structures.
[0024] In at least one embodiment, the surface features 70 may be
micro or nano features. Micro features may be those having a size
(e.g., width or diameter) of less than 1 mm and nano features may
be those having a size of less than 1 .mu.m. In one embodiment, the
surface features, such as cone-shaped or tapered cylinders, may
have a width or diameter (e.g., at their largest point) of less
than 500 .mu.m, for example, less than 250 .mu.m, 100 .mu.m, 50
.mu.m, 25 .mu.m, 10 .mu.m, 5 .mu.m, or 1 .mu.m. In another
embodiment, the surface features may have a width or diameter
(e.g., at their largest point) of 10 nm to 500 .mu.m, or any
sub-range therein, such as 10 nm to 100 .mu.m, 50 nm to 50 .mu.m,
100 nm to 10 .mu.m, 500 nm to 10 .mu.m, 1 .mu.m to 25 .mu.m, or
others. By varying the parameters of the laser, the surface
morphologies of the features may be controlled. In one example,
surface hydrophobicity may be varied along a flow path or at
certain geometric features by altering laser parameters such as
laser power, speed, and line of sight. For example, by controlling
one or more of the above parameters, a distal end of a via may be
made more or less hydrophobic than a proximal end (e.g., adjacent
the transition or active zone). The hydrophobicity may continuously
change along the via length or there may be two or more different
hydrophobicity regions.
[0025] The laser treatment may involve a layer-by-layer material
removal (e.g., ablation) process. The pulsed laser beam may be
scanned or rastered along the surface of the material to be treated
(e.g., an inner wall of an exit via) to progressively generate the
surface features. The surface to be treated may be scanned by the
laser multiple times. There may be several factors or parameters
that affect the creation of the surface features and the
hydrophobicity of the resulting surface morphology. For example,
the parameters may include the fluence of the laser (energy per
area), the pitch of the laser scan (.DELTA.d, center-to-center
distance), the scanning speed (v, e.g., mm/s), the number of layers
(N, e.g., times the surface is scanned), or others. In general, it
has been found that relatively greater scan speed and/or fluence
may increase the hydrophobicity of the resulting morphology.
Increasing the scan speed may result in a higher density of the
surface features (e.g., cones). As the density increases, the size
(e.g., diameter) of the surface features may be decreased. The
surface features shown, for example in FIGS. 5A and 5B, may result
in a hydrophobic coating having a contact angle with water of, for
example, at least 90 or 100 degrees. The same laser treatment may
also be used to make a metal surface more hydrophilic by adjusting
the parameters above (e.g., in the opposite direction).
[0026] Accordingly, in at least one embodiment, the internal
surfaces or walls of the vias 64 of the bipolar plate 50 may be at
least partially treated using a laser treatment. For example, at
least 50% of the internal surface area of at least one of the vias
64 may be laser treated, such as at least 60%, 70%, 80%, 90% or at
least 99%. In another embodiment, the entire internal surface of at
least one via 64 may be laser treated (e.g., 100%). One, some, or
all of the vias 64 may be treated in this way. For example, at
least 50% of the vias 64 may be treated as described above, such as
at least 75% or at least 90% of the vias 64 (by number). In another
embodiment, every via 64 may be laser treated. The above may apply
to inlet vias, outlet (exit) vias, or all vias in the bipolar
plate. Similarly, it may apply to the fuel vias (e.g., hydrogen),
the oxygen (e.g., air) vias, or both.
[0027] In one embodiment, at least every outlet/exit via 64 is
laser treated. The outlet vias may be substantially completely
treated (e.g., at least 95% by area). In the embodiments described
above, areas that are treated by the laser may be completely or
substantially completely (e.g., at least 95%) covered by the
surface features (e.g., cones or tapered cylinders). Therefore, the
areas described above may also be percentages of the vias covered
by the surface features. For example, if an outlet via is laser
treated on 80% of its area, then the surface features may cover 80%
of its area (e.g., the same area that was laser treated). While the
treatment areas and percentages described above refer to the vias
64, they may also apply to the channels 62 of the transition zone
58 and/or the channels 56 of the active area 52.
[0028] In another embodiment, the treatment may be a chemical
treatment, such as a chemical etching or chemical roughening
treatment (referred to hereinafter as just a chemical treatment).
The chemical treatment may produce surface features 70 having a
similar structure and/or size to those describes above (e.g.,
cone-shaped, stepped pyramid, etc.). The chemical or chemicals used
to treat the bipolar plate may depend on the bipolar plate
composition. Non-limiting examples of bipolar plate materials may
include aluminum, copper, and steel (e.g., stainless steel). The
chemical treatment may include treating the bipolar plate with a
strong acid or a strong base, such as HCl or NaOH, respectively (or
any of the known 7 strong acids and 8 strong bases). The chemical
treatment may include a single step or multiple steps. For example,
it may include a first step with a first chemical and a second step
with a second, different chemical. Additional steps and chemicals
may also be included. Chemicals other than strong acids/bases may
be included, such as ZnNO.sub.3, Cu(NO.sub.3).sub.2, AlCl.sub.3,
triethanolamine, La(NO.sub.3).sub.3, FeCl.sub.3, combinations
thereof, or others.
[0029] In one embodiment, the chemical treatment may be performed
by dipping at least a portion of the bipolar plate into a chemical
bath. For example, only a portion including the vias, but not the
transition or active zones may be dipped. In other embodiments, the
vias and the transition zone may be dipped, but not the active
zone. In another embodiment, the entire bipolar plate may be dipped
in the chemical treatment. Methods other than dipping may also be
used to apply the treatment. For example, the chemical treatment
may be sprayed onto the bipolar plate. If the bipolar plate is
formed in two halves, the inner surfaces may be sprayed before
assembling the plate. The chemical treatment may also be an
electrochemical treatment. Masking may be used to shield portions
of the bipolar plate from the treatment. In some embodiments, the
inner and outer surfaces of the vias may be treated (e.g., if the
plate is dipped). The chemical treatment may be performed at room
temperature or at other temperatures, such as an elevated
temperature.
[0030] The shape and the configuration of the vias 64 may vary
depending on the specific design of the bipolar plate 50. In some
embodiments, the vias 64 may be completely enclosed by the bipolar
plate itself, except for the entrance/inlet and the exit/outlet.
For example, the vias 64 may be tubes or conduits, and may have
substantially circular or rectangular cross-sections. In another
embodiment, the vias 64 may be defined by a corrugation between two
opposing sides of the bipolar plate. In this embodiment, the vias
may have a generally triangular cross-section. However, other
passage shapes are possible, such as oval or tapered, and the
passage shape in the present disclosure is not limited. The inner
surfaces of the vias 64 may be smooth on a macro-level (e.g., scale
above 1 mm), or they may include macro-level bumps or other
features. The macro-level features may increase the turbulence of
the gas flow or direct the gas flow during operation of the fuel
cell (e.g., to help improve cell pressure control). In some
embodiments, the vias 64 may include enclosed tubes or conduits
that are formed by two halves of the bipolar plate. In other
embodiments, there may be a cover sheet or cover plate that
overlies a channel or depression in the bipolar plate to form an
enclosed tube or conduit.
[0031] In one embodiment, the hydrophobic treatment may be applied
to the inner surface(s) of the vias 64, which may be the surface(s)
that define the passage through which fluid received from the
active area flows (e.g., air/fuel and generated water). The
treatment may be applied to all surfaces, including any macro-level
features. If the vias 64 are formed by two halves of a bipolar
plate, the halves may be treated prior to assembling or combining
the halves. However, if the treatment includes dipping the bipolar
plate into a bath, the halves may be already assembled during
treatment. If the vias 64 are at least partially formed by a cover
sheet or plate, the via-side of the cover sheet/plate may be
treated in a similar manner as the bipolar plate itself prior to
installation. In some embodiments, the inner surfaces may be the
only surfaces treated; however, in other embodiments the outer
surfaces of the vias 64 may also be treated. For example, if the
bipolar plate is treated by dipping it into a bath, then all
surfaces of the vias 64 and other portions of the plate may be
treated.
[0032] Accordingly, treated bipolar plates and methods of treating
bipolar plates are disclosed. The treated portions, such as inlet
or outlet vias, may be rendered hydrophobic and may reduce or
prevent water build-up. By avoiding the accumulation of water in
the vias, freezing and blocking of these typically small passages
may be reduced or avoided. Accordingly, freeze start-up procedures
may be reduced or eliminated, as well as the associated delay in
being able to operate a fuel cell vehicle. The treatment may result
in a surface that has a contact angle with water of at least 90
degrees, for example, at least 100, 110, 120, or 130 degrees. In
some embodiments, the treatments may result in a surface that is
super hydrophobic, having a contact angle with water of at least
150 degrees.
[0033] Based on the present disclosure, one of ordinary skill will
understand that the same surface texturing practices may be used to
produce hydrophilic surfaces on the bipolar plates. Furthermore,
hydrophobic surfaces could be combined with hydrophilic surfaces to
further tailor water management features on a bipolar plate. Making
bipolar plate surfaces hydrophobic and/or hydrophilic through
texturing to improve water management may allow for an alternative
stack build orientation compared to the common build orientations
(e.g., vertical). A horizontal stack build orientation
incorporating the disclosed treated bipolar plates may improve
in-vehicle stack packaging, reduce stack control system complexity,
and/or reduce related costs. Because a hydrophobic surface sheds
water easily, less pressure may need to be applied to eradicate
water from a cell, thus potentially allowing the compressor size
requirement of a system to be decreased. The natural characteristic
of a hydrophobic surface to shed water may also allow for fuel cell
stack unit cells to be stacked horizontally in a pancake scenario
with only the inlet and exhaust manifold ports being vertical. The
hydrophobicity of the textured surfaces would minimize the
influence of gravity to hold generated water in-on-along the plate
geometries and flowing gases could easily eradicate remaining water
during shut down.
[0034] While exemplary embodiments are described above, it is not
intended that these embodiments describe all possible forms of the
invention. Rather, the words used in the specification are words of
description rather than limitation, and it is understood that
various changes may be made without departing from the spirit and
scope of the invention. Additionally, the features of various
implementing embodiments may be combined to form further
embodiments of the invention.
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